Loss of smell in patients with Covid-19 may be due to the persistence of the virus in the nasal cavity, says a study published in “Science Translational Medicine.”
The SARS-CoV-2 virus can persist in smell-sensing neurons in some Covid-19 patients for several months after infection, affecting the ability of cells to function, according to an analysis of 11 patients and hamsters. .
The results may help explain why many Covid-19 patients lose the ability to smell or taste, a symptom that can remain after others have remitted.
Over the past year, researchers have learned a lot about how SARS-CoV-2 impacts cells and organs in the body. However, certain aspects of the disease remain a mystery.
One of the most common symptoms of Covid-19 is loss of smell or taste, and studies suggest that this symptom sometimes lasts for months after the acute phase of infection.
But scientists are not sure why and how the virus affects the olfactory system at the cellular and molecular level.
Using non-invasive nasal brush sampling, Guilherme Dias de Melo and his team from the Pasteur Institute (France) analyzed the neuroepitelio olfatorio, a specialized lining of odor-sensitive cells within the nasal cavity, in 7 mild Covid-19 patients who reported loss of smell.
The researchers found that SARS-CoV-2 infected and replicated in smell-sensitive neurons, immune cells, and other cell types in the neuroepithelium, causing inflammation and cell death.
In addition, hamsters infected with SARS-CoV-2 showed viral presence in the olfactory epithelium and in the brain, as well as a loss of taste and smell during feeding experiments, which lasted until the virus became undetectable in the neuroepithelium of animals.
The researchers also detected persistent SARS-CoV-2 RNA in the neuroepithelium of 4 other patients with prolonged loss of smell due to Covid-19, which had not been detected in standard tests of nasopharyngeal samples.
Although studies with larger patient groups are needed, the authors suggest that loss of smell could be interpreted as a sign of persistent viral infection during clinical treatment.